13-06-2022 | | By Robin Mitchell
Recently, researchers from NTU Singapore have developed a wearable flexible fabric that can generate electricity when under deformation. What challenges have wearable energy sources faced, what did the researchers develop, and how does this demonstration differ from others?
When discussing wearable technologies, it is important to clearly define what classifies a wearable device. Depending on who is asked, some will classify a wearable device as anything that is worn, including smartwatches, while others will argue that wearable devices are those specifically worn on the body (not just the wrist).
Regardless of whether a smartwatch is considered wearable or not, what can be said for any wearable device is that it must be comfortable. This hasn’t been an issue for smartwatches as they are worn on the wrist, but when it comes to clothing and other bodily accessories, this has proven to be a significant challenge. The ridged nature of electronics means that they cannot flex and bend with the body, and thus most off-the-shelf circuits are noticeable when integrated into clothing.
However, another challenge that researchers have faced is energy generation for wearable devices. Great strides have been made in developing flexible circuits, but getting power is difficult for a multitude of reasons. Firstly, most battery technologies are ridged, meaning that attaching a bulky battery to a piece of material is extremely uncomfortable.
Secondly, wearable flexible energy sources that have been developed have been demonstrated to generate minute amounts of power. While such energy sources may be able to power a sensor, they cannot power more complex devices such as microcontrollers and wireless communication modules.
Thirdly, many wearable energy sources have only been demonstrated to operate under ideal conditions. For example, researchers recently developed a wearable Thermoelectric Generator (TEG), but the energy generated was so small that it would require a 40˚C gradient between the wearer and the surrounding environment to produce any usable amounts of power.
Finally, many wearable solutions have been unable to withstand washing cycles, which is required for any clothing. No number of embedded sensors and microcontrollers will make a t-shirt popular if it cannot be washed.
Recently, researchers from NTU Singapore announced their development of a wearable fabric able to generate electricity from movement. The material was constructed using a polymer with piezoelectric properties (i.e., generating electricity under mechanical stress) that is impregnated into a layer of spandex that integrates rubber-like materials to allow for flexibility.
Not only does the material generate energy when stretched, but the polymer also has triboelectric properties meaning that it generates energy under friction. Thus, skin movement underneath the fabric also generates energy which helps boost the material’s energy harvesting abilities.
To demonstrate the fabric’s ability, the researchers showed how a 3cm x 4xm sheet of the fabric could power 100 LEDs, and the results from this experiment show that the fabric has an approximate energy generation of 2.34 watts per square meter. Furthermore, the researchers also demonstrated the ability for the fabric to be machine washed, folded, and crumpled while showing no signs of performance degradation even after five months.
Research papers on wearable sensors and devices are often reported in the media with promises of grandeur and ground-breaking technological changes. Still, the truth is that most are unsuitable for commercial applications, cannot generate useful amounts of energy, or only operate under laboratory conditions.
However, researchers from Singapore have a real chance of making a genuine commercial breakthrough in the field of wearable electronics. Firstly, the material demonstrating an energy generation of 2.34W/m2 is more than enough to power most commercial microcontrollers, wireless modules, sensors, and interfaces. Combined with energy harvesting technology, the material could easily be used in various applications, including medical sensors, sports monitors, and general health tracking.
Considering that the fabric can be machine washed and show no signs of degradation after five months, it may be an ideal power source for future wearable devices. It would seem that the next step for the researchers is to turn the fabric into a piece of clothing and then integrate devices into the material. If done, this could be one of the first truly wearable pieces of electronic clothing.